Soldering in a reflow furnace generally employs solder paste. In soldering using a solder paste, first, the solder paste is applied to portions to be soldered of a printed circuit board with a printing device or dispenser, and electronic parts are placed on the portions where the paste was applied. The printed circuit board on which the electronic parts were placed is then heated in a reflow furnace to melt the solder paste and solder the printed circuit board and the electronic parts to each other.
A reflow furnace for soldering printed circuit boards is constituted by a preheating zone, a main heating zone, and a cooling zone. In order to carry out soldering, a printed circuit board to which a solder paste is applied is preheated by a heater in a preheating zone, it then undergoes main heating by a heater in the main heating zone, and it is cooled by a cooler in the cooling zone.
Solder paste is a viscous, pasty material obtained by mixing solder powder and a flux. Flux used in solder paste includes solid constituents such as rosin, an activator, and a thixotropic agent dissolved in a high boiling point solvent. Accordingly, when a printed circuit board to which a solder paste is applied is heated in a reflow furnace, it is first heated to 100-150° C. by a heater in the preheating zone, causing the solvent in the solder paste to evaporate and the solid constituents of the flux to melt. The molten solid constituents of the flux act to reduce and remove oxides adhering to the printed circuit board, thereby cleaning portions to be soldered. The printed circuit board is then heated to at least 200° C. by a heater in the main heating zone, and the solder powder melts and spreads over the cleaned portions to be soldered. After the molten solder has sufficiently spread over the portions to be soldered, it is cooled by a cooler in the cooling zone, and the molten solder is solidified to complete soldering.
Solder paste which is applied to a printed circuit board generates fumes by vaporization of solvent in the preheating zone. In addition, when solid constituents of the flux which melt in the preheating zone are exposed to a high temperature in the main heating zone, they become fumes. These fumes float inside the furnace. If these fumes of solvent and solid constituents contact components inside the furnace which are at a relatively low temperature, such as a conveyor which transports printed circuit boards inside the furnace, a fan which circulates hot air, a frame which forms the furnace, or labyrinths installed at the entrance and exit of the furnace, the fumes are cooled and condensed, and when the temperature further decreases, they become sticky solids. If a large amount of fumes which have become solids (referred to below as fume solids) adhere to components of the reflow furnace, they cause problems. Namely, if a large amount of fume solids adheres to a conveyor, printed circuit boards will adhere to the conveyor and will not separate from the conveyor when being transported out and will become entangled in the sprockets of the conveyor, resulting in damage to the printed circuit boards. If a large amount of fume solids adheres to a fan, the rotational speed of the fan will decrease and the strength with which air is blown will become weak. If a large amount of fumes solids adheres to a frame, the accumulated fume solids will drop onto printed circuit boards being transported and contaminate the printed circuit boards. Furthermore, if a large amount of fumes solids adheres to a labyrinth, the fume solids will contact printed circuit boards and cause electronic parts to drop off from prescribed locations.
In light of these problems resulting from adhesion of fume solids, from in the past, there have been many proposals of methods and apparatuses for removing fumes from inside a furnace (Patent Documents 1-8). A conventional reflow furnace with a fume removal mechanism had a fume removal device installed in a location separated from the furnace, and fume removal was carried out by lowering the temperature of fumes discharged by a pipe from the interior to the exterior of the furnace to as low a temperature as possible and condensing the fumes.
Patent Document 1: JP H04-13475 A1
Patent Document 2: JP H04-46667 A1
Patent Document 3: JP H04-251661 A1
Patent Document 4: JP H07-77346 A1
Patent Document 5: JP H07-212028 A1
Patent Document 6: JP H10-335807 A1
Patent Document 7: JP S54-41411 U1
Patent Document 8: JP S64-20964 U1